Antenna for microwave beacons



A 26, 1952 N. KORMAN 2,608,659

ANTENNA FOR MICROWAVE BEACONS Filed Jan. 10, 1948 INVENTOR NATHANIEL I; KOR MAN BY F l ,ATTO NEY EPatented Aug. 26, 1952 ANTENNA FOR MICROWAVE BEACONS Nathaniel I. Korman, Camden, N. J assignor to Radio Corporation of America, a corporation of Delaware I Application January 10, 1948, Serial No. 1,634

7 Claims- (CL 250-33.63)

The present invention relates to microwave antenna and more particularly to such antennas adapted for broadcast service over a wide range of frequency.

An object of the presentinvcntion is the provision of a simple'antenna structure for microwave use giving high, vertical directivity.. Another object of the present invention is the provision of an antenna as aforesaid which has substantially no horizontal, directivity and which is relatively non-frequency selective. Afurther obiect of the present invention is the provision of a microwave antenna forbroadcast use which provides essentially a'narrow vertical beam of radiated energy with a definite amounto'f high angle coverage. 'Still another object of the present invention is theprovisionof an arrangement for coupling a wave guide or transmission line to free space to radiate horizontally polarized wave energy of equal intensity in all directions in the meridian plane.

The foregoing objects, and, others which may appear from the following detailed description are attained by providing a relatively non-directional source of high frequency'energy with a slatted lens array which brings into focus the radiation in a narrow vertical beam. The slatted lensis so constructed that there is'substantially no focusing in the horizontal'plane. Thus the antenna is well suited to broadcast transmission of microwave signals. f

For the sake of convenience, in the following detailed description, the antenna will be described scription which isacccmpanied by a drawing in which Figure 1 illustrates in elevation and partly in section an embodiment of the present invention; while Figure; illustrates in section a modification of a portion of the structure of Figure 1; Figures 3, 4 and 5 illustrate in section further modifications or the slatted lens structure of Figure 1; while Figure'G illustrates'in enlarged perspective view a preferredform of non-directional radiant energy source adapted to be used with the slatted antennasof Figures 1 to Sinclusive.

Referring now to Figure 1, I have shown a relatively non-directional source of high frequency energy A, located on the axis of a cylindrical slatted lens B. The slatted lens B is composed of a large number of fiat'metallic discs or rings ID, having central apertures 12 of varying sizes. The spacing between the discs or rings In is. sorelated to the operating wave length of the system that the electromagnetic waves originatin at source A assume, between the plates, a wavelength and phase velocity whichis greater than their free space wave length and velocity. Ordinarily this spacing is of the order of; but somewhat greater than one-half of the operating wave length. The plane in which plates or discs Ill lie must be parallel to the electric vector of the wave emitted by source A.

.The stack of plates or discs [0 thus constitute a refractive'medium with an index of refraction less than unity. Since, ina radial direction from source A, the amount of phase advance imparted to the Waves by thespaces between the discs ID at the ends of the cylinder is greater than at intermediatepoints along the cylinder, the assembly of rings produces a focusing of waves that is similar to that effected by a cylindrical lens about a point source of light. Thus the radiation emitted from source A is compressed in the vertical plane. Due to the fact that the rings are symmetrical about the axis on which source A lies, no focusing effect is obtained in the horizontal plane.

Since the lens of Figure 1 tends to become very thick at the ends of the cylinder a modified form of the invention is illustrated in Figure 2 wherein the diameter of the inner holes in rings HJ vary in steps of multiples of a wavelength. The remainder of the structure used with the lens of Figure 2 is the same as described in Figure 1.

In Figure 3, I have shown in diagrammatic form a further modification of my invention in which, instead of graduating the length along the direction of wave travel, of constant spacing slots, I use a graduated spacing of constant length slots. In this form the rings l0 have constant diameter innerapertures while the spacing between the rings at each end of the cylinder is closer than at intermediate points along the cylinder. Due to the narrower spacing at the ends of the cylinder an increased wave velocity is obtained over that Whichoccursfat intermediate points along the cylinder.

In the lens of Figures 1, 2 and 3 a certain amount of power is reflected from both lens faces. From the standpoint of power efiiciency, these refiections are not too important. However, it is important that not much of the reflected power be returned directly to the source A because ofthe standing waves which would thus be caused to occur within the transmission line or wave guide TL. The surface of the lens formed by the apertures in rings ii] does not ordinarily cause much trouble on this account, because the reflected power from it is ordinarily scattered and not focused back on source A. However, the outer surface of the cylinder B can reflect a serious amount of power into A. Therefore, in Figure 4, instead of having the outer face cylindrical, the outer surface of lens B is formed as a truncated cone tapering from one end to the other as indicated by the angle marked a. in Figure 4.

As a further modification instead of using a truncated cone, a stepped cylinder such as shown in Figure 5 may be employed. Here the lens B has one series of rings [0 having one outside diameter and a second series 20 of a different outside diameter. The diameters of the inside apertures in rings it and 29 must be correspondingly adjusted as indicated in the figure.

A further feature of the present invention includes the addition of absorbing material C on the outside surface of the wave guide TL to absorb energy reflected from the outer surface of rings B back toward the source A. This absorbing material may be in the form of a relatively thick coat of poorly conductive material such as conductive rubber.

In Figure 6, I have shown in somewhat enlarged form the relatively non-directional source A of Figures 1 to 5 inclusive. As indicated in Figure 6 a circularly polarized wave of the TE1,1 mode is set up in the round wave guide TL by methods well known in the art. Four longitudinal slots 40 each approximately a half-wave in length are cut in the outer surface of the wave guide TL. The slots 40 are uniformly ninety degrees around the circumference of the wave guide.

Radiant energy within the wave guide TL is coupled with surrounding space to radiate a high frequency wave of equal intensity in all directions of the meridianal plane. The vertical directivity of the antenna of Figure l energized from a nondirectional source such as that shown in Figure 6, is about the same as would be obtained at lower frequencies from a two layer tumstile antenna.

It is to be understood that other non-directional sources known to those skilled in the art may be used in place of that shown in Figure 6.

What is claimed is:

1. An antenna to be operated at a definite operating frequency and comprising a central radiator or receptor for radio waves at said frequency and having a radiation pattern substantially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disc-like with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct communication with the central space defined by said central apertures and within which said central radiator or receptor is positioned, the axial spacing between plates and the dimension of each plate radially from said inner to said outer edge being selected to cause a relative shift in phase between radio waves at the operating frequency polarized with the electric vector normal to said axis and thus parallel to said plates and propagated radially between one pair of adjacent plates and those similarly polarized and similarly propagated between an adjacent pair of plates, said shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said central plates, whereby the said antenna is nondirectional in a plane normal to said axis, and the directivity in a. plane through said axis is increased over that of said central radiator or receptor, said outer edges lying on a truncated conical surf-ace coaxial with said axis, whereby reflections are reduced.

2. An antenna to be operated at a definite operating frequency and comprising a central radiator or receptor for radio waves at said frequency and having a radiation pattern substantially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disc-like with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct communication with the central space defined by said central apertures and within which said central radiator or receptor is positioned, the axial spacing between plates and the dimension of each plate radially from said inner to said outer edge being selected to cause a relative shift in phase between radio Waves at the operating frequency polarized with the electric vector normal to said axis and thus parallel to said plates and propagated radially between one pair of adjacent plates and those similarly polarized and similarly propagated between an adjacent pair of plates, said shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said central plates, whereby the said antenna is nondirectional in a plane normal to said axis, and the directivity in a plane through said axis is increased over that of said central radiator or receptor, said outer edges lying on a truncated conical surface coaxial with said axis, whereby reflections are reduced, the inner edge radii being progressively larger from the plates centrally located along the axial direction with axial distance from the central plates.

3. An antenna to be operated at a definite operating frequency and comprising a central radiator or receptor for radio waves at said fre quency and having a radiation pattern substan tially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disc-like with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct communication with the central space defined by said central apertures and within which said central radiator or receptor is positioned, the axial spac ing between plates and the dimension of each plate radially from said inner to said outer edge being selected to cause a relative shift in phase between radio waves at the operating frequency polarized with the electric vector normal to said axis and thus parallel to said plates and propagated radially between one pair of adjacent plates and those similarly polarized and similarly propagated between an adjacent pair of plates, said shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said centr'aILpIates, whereby the said antenna is nondirectional in a plane normal to said axis, and thedirectivity in a plane through said axis is increased over that of said central radiator or receptor, said outer edges on one side of the plates centrally located along the axial direction, being all of one radius, and those on the other side axially of said central plates being of the same radius different from said one radius, whereby reflections are reduced.

4. An antenna to be operated at a definite operating frequency and comprising a central radiator or receptor for radio waves at said frequency and having a radiation pattern substantially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disc-like with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct communication with the central space defined by said central apertures and within which said central radiator or receptor is positioned, the axial spacing between plates and the dimension of each plate radially from said inner to said outer edge being selected to cause a relative shift in phase between radio waves at the operating frequency polarized with the electric vector normal to said axis and thus parallel to said plates and propagated radially between one pair of adjacent plates and those similarly polarized and similarly propagated between an adjacent pair of plates, said i shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said central plates, whereby the said antenna is nondirectional in a plane normal to said axis, and the directivity in a plane through said axis is increased over that of said central radiator or receptor, the outer and inner edge radii of any plate on one side axially of a plane centrally located along and normal to said axis, each being less by the same amount than the respective outer and inner edge radii of a plate an equal distance on the other side of said central plane.

5. An antenna to be operated at a definite operating frequency and comprising a central radiator or receptor for radio waves at said frequency and having a radiation pattern substantially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disclike with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct communication with the central space defined by said central apertures and within-which said central radiator or receptor is inner 'to said outer edge being selected to cause a relative'shift in phase between radio waves at the operating frequency polarized with the: electric vector normal to said axis and thuspalr allel to said plates and propagated radially be tween one pair of adjacent plates d those similarly polarized andsimilarly propagated, between" an adjacent pairof'plates said shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said central'plates, whereby the said antenna is'non-directional in aplane normal to said-axis, and the directivity in a plane through said axis is increased over that of said central radiator or receptor, the outer edge radii being different to-Vreduce reflections, the spacing and inner edge radii being selected to secure the said relative phase shift.

6. An antenna to be operatedata definite operating frequency and comprising a central radiator or receptor for radio waves at said frequency and having a radiation pattern substantially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disc-like with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct communication with the central space defined by said central apertures and within which said central radiator or receptor is positioned, the axial spacing between plates and the dimension of each plate radially from said inner to said outer edge being selected to cause a relative shift in phase between radio waves at the operating frequency polarized with the electric vector normal to said axis and thus parallel to said plates and propagated radially between one pair of adjacent plates and those similarly polarized and similarly propagated between an adjacent pair of plates, said shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said central plates, whereby the said antenna is nondirectional in a plane normal to said axis, and the directivity in a plane through said axis is increased over that of said central radiator or receptor, the said radiator or receptor including on its surfaces exposed to said plates radio wave energy absorbent material to reduce multiple reflections.

7. An antenna to be operated at a definite (JD-7 crating frequency and comprising a central radiator or receptor for radio waves at said frequency and having a radiation pattern substantially non-directional about a predetermined axis, a stack of more than two substantially parallel metallic plates surrounding and spaced from said radiator or receptor and spaced in the axial direction each from the next adjacent plate by more than a half free-space wavelength at the operating frequency, each said plate having a central aperture and being disc-like with inner and outer edges each substantially a complete circle coaxial with said axis, the space between each adjacent pair of plates being in direct coinmunication with the central space defined by said central apertures and within which said central radiator or receptor is positioned, the axial spacing between plates and the dimension of each plate radially from said inner to said outer edge being selected to cause a relative shift in phase between radio waves at the operating frequency polarized with the electric vector normal to said axis and thus parallel to said plates and propagated radially between one pair of adjacent plates and those similarly polarized and similarly propagated between an adjacent pair of plates, said shift in phase at plates centrally located along said axis being progressively less than and in retardation of those more remote from said central plates, whereby the said antenna is nondirectional in a plane normal to said axis, and the directivity in a plane through said axis is increased over that of said central radiator or receptor, the inner edge radii being staggered to secure at selected axial plates at full wavelength difference in addition to said phase retardation, thereby to reduce the bulk of the stack of plates from what it otherwise would be.

NATHANIEL I. KORMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS OTHER REFERENCES Metal-Lens Antenna, Free. I. R. E., by W. E. Kock.

Metallic Delay Lenses, by W. E. Kock, Bell System Technical Journal, vol. 27, pages 58 to 82, January 1948.

Radio News, November 1947, pages 3, 4, 5 and 20.

Electronics, February 1947, pages 90 to 93. 

